#!/bin/bash

function split(){
  local src="$1"
  local dst="$2"
  local start="$3"
  local duration="$4"
  
  # ffmpeg param "-n"
  # Do not overwrite output files, and exit immediately if
  # a specified output file already exists.


  if [ "$4" -gt 0 ] ; then
    # Take section from (start) to (start + duration)
    ffmpeg -n -i "${src}" -ss "$start" -t "${duration}" -c copy "${dst}"
    errno="$?"
  else
    # $4 is empty or <1
    # Take section from (start) until (end of video)
    ffmpeg -n -i "${src}" -ss "$start" -c copy "${dst}"
    errno="$?"
  fi
  
  return "$errno"
}

function isPositiveInt(){
  # https://stackoverflow.com/a/3951175/6334421
  case "$1" in
    ''|*[!0-9]*) return 1 ;;
    *) return 0 ;;
  esac
}

function main(){
  # TODO: check if ffmpeg installed

  local source="$1"
  local seconds="$2"
  
  # if args are empty -> cancel
  if [ "$#" -ne 2 ] || [ -z "$1" ] || [ -z "$2" ] ; then
    echo "Error: Expected two non-empty arguments!"
    echo "usage: $0 <source> <seconds>"
    exit 1
  fi
  
  if ! isPositiveInt "$2" ; then
    echo "2nd arg must be positive integer"
    return 2
  fi

  split "$source" "${source}_a.mkv" "0" "$seconds" || exit "$?"
  split "$source" "${source}_b.mkv" "$seconds"
  exit "$?"
}

main "$@"